Antedating patent

The current American version of the grounded plug, with two vertical blades and a round grounding pin was invented by Philip F.Labre, while he was attending the Milwaukee School of Engineering (MSOE).Sometimes offshore industrial plants or overseas military bases use the wiring practices of their controlling country instead of the surrounding region.Hotels and airports may maintain receptacles of foreign standards for the convenience of travellers.

The original socket into which the user inserted the appliance's plug (of Hubbell's design) itself screwed into the sort of socket used for light bulbs, rather than being directly connected to the building's fixed wiring.(US Patent #774,250) Other manufacturers adopted the Hubbell pattern and by 1915 they were widespread, although in the 1920s and even later, household and light commercial equipment was still powered through cables connected with Edison screw-base adapters to lampholders.The grounded consumer plug has several claimants to its invention.To reduce the risk of electric shock, plug and socket systems can incorporate a variety of safety features.

For example sockets can be designed to accept only compatible plugs and reject all others.

The earliest patent for a grounded plug appears to be one applied for on January 11, 1915 by George P.